Manufacture of artificial sponges



Patented Sept. 18, 1934 UNITED STATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL SPONGES No Drawing. Application December 27, 1932, Serial No. 649,114. In Germany December 28,

8 Claims. (01. 18-48) My present invention relates to the manufacture of artificial sponges and more particularly to the manufacture of such sponges from viscose.

One of its objects is to provide an improved process for the manufacture of artificial sponges from viscose. Further objects will be seen from the detailed specification following hereafter.

It is known to produce artificial sponges from viscose by mixing viscose with a pore-forming l0 material and a fibrous material by coagulating and decomposing the cellulose xanthogenate into cellulose hydrate while simultaneously removing the pore-forming material. The regeneration of the cellulose is effected by the action. of acid or salt solutions, hot air or water vapour.

The regeneration of the cellulose by the application of steam has also been effected by causing the steam to act upon a mixture of viscose and an easily fusible or water soluble substance under 20 pressure.

According to my present invention artificial sponges are manufactured from a molded mixture of viscose and suitable pore-forming fillers by regenerating the cellulose from the viscose in a liquid regeneration bath under pressure.

The pressure forces the preferably hot regenerating liquid into the molded mass with the advantage that the latter may be of a considerably larger size than the masses hitherto converted into sponge, without imperiling the homogeneity of the sponge obtained. Moreover, the operation of producing the sponge is shortened, so that the formation of waste material (so-called incrustations) is reduced.

The molded mass which is to be converted into sponge consists of a mixture of viscose and a substance capable of forming the pores of the sponge, and, if desired, of dyestuffs or fibrous materials or both. There is the further advantage that together with the regenerating liquid which is forced in under pressure into the sponge mass, additions may be introduced which during the formation of the sponge by the coagulation of the viscose and itsregeneration into cellulose hydrate are incorporated in the material of the sponge and are retained therein. Such additions may, for instance, be disinfectants, scents or the like.

Such additions incorporated in the sponge in the manner described add greatly to the value of the artificial sponge, as they are much more slowly removed therefrom by use, than for instance, in case the cellulose is regenerated by means of gaseous media and additions of the kind described are incorporated by a subsequent impregnation. Furthermore, by addition of suitable agents to the regeneration bath, it is possible to bleach the spongy mass already during its manufacture.

I have furthermore found that the regeneration baths which give the best result for the purpose in question are weakly alkaline solu tions. By the use of such baths the raw sponge mass, particularly as regards the pore-forming filler, becomes more independent of the degree of ripeness of the viscose (i. e. of the amount of the alkali set free and the speed of the liberation of the alkali from the xanthate). By a greater liberty in selecting the composition of the sponge mass it becomes possible to keep the mass in a more liquid condition. This not only facili tates the introduction of the sponge mass into the moulds, but prevents any premature partial coagulation in the mass caused by the use of anhydrous or nearly anhydrous salts as pore-forming fillers, which can be completely dispensed with. Furthermore, by maintaining a feebly alkaline reaction of the regeneration bath during the regeneration operation, there is prevented the occurrence of a non-uniform shrinking of the moulded article.

The degree of alkalinity or the upper limit of concentration in alkali of the regeneration baths may be easily determined by experiment, it must, however, not be too high as the action of concentrated alkali notoriously produces an undesired degradation of the cellulose molecule. The highest applicable concentration depends on the several working conditions, especially on the temperature used, because the higher the temperature, at which the regeneration is performed, the smaller the amount of free alkalithe baths should contain. With a regeneration bath containing about 1% of'free caustic soda solution or an equivalent amount of another base, under normal conditions, I have obtained good results. There may, however, also be used considerably lower alkali concentrations, and if required, also higher concentrations.

As regenerating baths, saturated salt solutions have proved to be particularly suitable in order to prevent premature removal of the pore-forming fillers from the sponge mass. During the regeneration or immediately after its completion the solutions may be diluted. In this way the The described treatment of the sponge mass, effected under pressure, may be followed by a vacuum treatment, it being advantageous, to keep the sponge mass, during the mixing operation at a reduced pressure, or to expose the sponge mass ready for coagulation in the mould to the action of reduced pressure prior to the action of the liquid regenerating baths.

This expedient allows one to treat the spongeforming masses while in a thinly liquid condition in which they can easily be mixed and moulded, whereas the concentrations most favorable for the further treatment of the sponge masses are only attained in the course of the mixing or moulding step by the action 'of the vacuum. Moreover this process involves the possibility of conducting the manufacture in such a manner that the viscose, in the production of the porous structure, is not directly regenerated .into cellulose hydrate, but is only gradually converted into cellulose hydrate during the further treatment whereby the coagulation and the decomposition occur in successive steps. Thus, for instance, a moulded mass from viscose and pore-forming fillers is dehydrated by heating in the vacuum to such an extent, that the body precipitated mainly consists of non-decomposed xanthate, which then by the action of the liquid baths under pressure is decomposed into cellulose hydrate. The properties of the articles obtained in respect of touch, elasticity and tensile strength are greatly improved by the treatment' according to this invention.

The following example serves to illustrate the invention:

120 kg. of a viscose solution containing 4-5 per cent of cellulose and prepared while preventing degradation of the cellulose as much as possible by shredding the alkali cellulose at a low temperature and without ripening the alkali cellulose and the viscose are, if required after addition of dyestuffs, intimately mixed with 300 kilos of grains of sodium sulphate of various sizes and 30 kilos of an artificial or a natural fibrous material, such as staple fibers, flax, jute, ramie fiber or coco fiber. It is advisable to cause greasy fibrous materials to swell previously in an alkaline solution containing at the most 10% of alkali. The pasty mass obtained is introduced into open moulds of a suitable material and then kept at a raised temperature under reduced pressure until the whole of the mass has coagulated. These bodies which have been molded under a reduced pressure are then exposed to the action of a regenerating bath consisting of a saturated solution of sodium sulphate, containing 1% of free caustic soda solution, and treated for A; to 2 hours under a pressure of up to '20 atmospheres. The regeneration bath may contain additions of scents or disinfectants. The articles obtained by the regeneration are, if required, bleached and dyed and finally made into smaller pieces of the desired shape.

My invention is not limited to the foregoingexample nor to the specific details given therein. Any viscose suitable for the production of artificial silkmay be used with my process, however, it is advantageous to use an unripened viscose made from unripened alkali cellulose. The temperature to he used in the treatment under reduced pressure as well as in the regeneration process may vary within wide limits. For the treatment under reduced pressure I have found suitable temperatures from about 20 to 30 and for the regeneration from about to 150, without limiting my invention thereto. Other concentrated salt solutions than that of sodium sulfate likewise are suitable, for instance, a solution of a sodium halide, potassium halide an earth alkali-metal halide, sodium sulfite, potassium sulfate, magnesium sulfate or of a salt of an organic acid, for instance sodium formate or sodium acetate sodium lactate etc.

The products obtained according to the process of this invention are primarily excellent substitutes for natural sponges. The porous structures may, however, also be used for other purposes, for instance as filter masses, heat insulators, packing material or sound absorbers.

What I claim is:

1. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore forming fillers to the action of a liquid regeneration bath under pressure.

2. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore-forming fillers to the action of a liquid regeneration bath containing a compound of the group consisting of disinfectants and scents under pressure.

3. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore-forming fillers to the action of a liquid regeneration bath having a weakly alkaline reaction, under pressure.

4. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore-forming fillers to the action of a liquid regeneration bath containing at the most 1 per cent of caustic soda, under pressure.

5. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore-forming fillers to the action of a concentrated solution of sodium sulfate containing 1 per cent of caustic soda, under pressure.

6. A process of manufacturing artificial sponges from viscose which comprises subjecting a mixture of viscose and pore-forming fillers to the action of a concentrated solution of sodium sulfate containing 1 per cent of caustic soda, under pressure and washing immediately after the regeneration.

7. A process of manufacturing artificial sponges from viscose which comprises subjecting to a reduced pressure a mixture of viscose and poreforming fillers and subjecting the mixture thus treated to the action of a liquid regeneration bath under pressure.

8. A process of manufacturing artificial sponges from viscose which comprises subjecting to a reduced pressure and heat a mixture of viscose and pore-forming fillers and subjecting the mixture thus treated to the action of a liquid regeneration bath under pressure.

HANS MOSTNY. 

